Process for the fibrous esterification of cellulose employing homogenizers



Patented Jan. 5, 1937 UNITED STATES PATENT OFFICE PROCESS FOR THEFIBROUS ESTERIFI- OATION F CELLULOSE EMPLOYING HOMOGENIZERS Louis M.Minsk, William O. Kenyon, and Harry Le B. Gray, Rochester, N. Y.,assignors, by mesne assignments, to Eastman Kodak Company, Jersey City,N. J., a corporation of New The present invention relates to a processof esterifying cellulose in fibrous form in a bath in which an aliphaticor alicyclic hydrocarbon is employed as the non-solvent and ahomogenizer is present to assure compatibility of the constituents ofthe bath.

Among the most efiective non-solvents known for the fibrousesterification of cellulose are the saturated hydrocarbons eitheraliphatic or alicyclic such as hexane or heptane mixtures orcyclohexane.

Some of these non-solvents are known under various names such asligroin, petroleum ether, Stoddard solvent, kerosene, gasoline, naphthaetc. In cases where these saturated hydrocarbon nonsolvents are employedfor esterifying cellulose the amounts necessary to assure insolubilityof the resulting ester in the esterification bath are much less than isthe case with the non-solvents which are ordinarily employed. However,these nonsolvents suffer the disadvantage that their mixture with thefatty acid anhydrides are heterogeneous especially in those cases wherehydrocarbons having a high boiling range are employed. This is true eventhough a quite small amount of fatty acid might be present.

It is possible to prepare a cellulose ester in an esterification bath inwhich an aliphatic hydrocarbon is employed as the non-solvent in whichno homogenizer is employed however the esterification is not uniform,the cellulose is severely degraded and the product, instead of being infibrous form as should be the case in a fibrous esterification process,is usually in the form of a powder which is worthless for thepreparation of film or sheets. By our process on the other hand analiphatic hydrocarbon may be employed as thenon-solvent but theesterification is uniform and the product is substantially undegradedand is valuable commercially.

One object of our invention is to provide a process for the fibrousesterification of cellulose in which a saturated hydrocarbon may beemployed as the non-solvent and in which the bath is homogeneous.Another object of our invention is to provide a process for the fibrousesterification of cellulose embodying all the advantages inherent in theuse of a saturated hydrocarbon but in which all the reagents therein arecompatible so that a uniform esterification of the cellulose is assuredand an undegraded product which may be employed for the manufacture ofsheets or film is obtained.

We have found that a fibrous esterification bath in which a saturatedhydrocarbon is the non-solvent, may be rendered homogeneous by theaddition thereto of an homogenizing agent. We have found that the lowerfatty acids or the ethers when added in a substantial amount willhomogenize the mixture of reagents which go to make up a fibrousesterification bath. Aromatic hydrocarbons such as benzene, toluene orcymene and halogenated hydrocarbons such as ethylene chloride or thelike also find use as homogenizers in accordance with our invention, theuse of the aromatic hydrocarbons as homogenizers being disclosed andclaimed by Yackel and Kenyon in their application Serial No. 671,899,filed of even date and the use of chlorinated hydrocarbons ashomogenizers is disclosed and claimed by Malm and Fletcher in theirapplication Serial No. 671,901, filed of even date.

In a fibrous esterification process in which a saturated hydrocarbon isemployed as the nonsolvent, a surprisingly small proportion of thathydrocarbon is necessary to render the esterification bath non-solventof the cellulose ester formed, however, the non-solvency of this liquidis so pronounced that it extends even to constituents of theesterification bath. By the present invention the effectiveness of thesaturated hydrocarbon to induce non-solvency of the cellulose ester bythe esterification bath may be ultilized and a uniform undegradingesterification of the cellulose is assured.

The following table shows the amount of the particular homogenizer whichis necessary to assure homogeneity in the given esterification bath.Obviously in instances where a difierent ratio of anhydride tohydrocarbon non-solvent is used, the amount of homogenizer may differfrom that given, however, that amount will be determined by theeffectiveness of the homogenizer. For example 6 parts of acetic acidwould be'required where only parts of propionic acid (by volume) wouldbe sufficient to homogenize an esterification bath. The parts given inthe table are all based on volume.

Amount of homogenizer Saturated Acetic anhydrocarbon hydride Egg???effect Parts Parts 2/0 5 parts benezene. 20 10 5 parts toluene. 20 10 6parts xylene. 20 10 6 parts ethyl ether. 20 10 5 parts propionic acid.20 10 6 parts acetic acid.

In some esterification processes acetic or propionic acid might bepresent and in that case it is only necessary to add sufiicient acid orother homogenizer to supplement the efiect of the organic acid presentif it is present in insufficient amount to assure homogeneity of theesterification bath.

The following examples illustrate the application of our invention tothe preparation of organic acid esters of cellulose.

Example I 20 lbs. of refined cotton linters was pretreated for 16 hrs.at room temperature with 140 lbs. of propionic acid containing 1.5 lbs.of mixed catalyst (1 part by volume concentrated H2SO4I3 parts 95%HaPOl). The mass was then pressed until the total weight of linters andacid was lbs. The esterification was then promoted by adding a mixtureof 50 lbs. of acetic anhydride and lbs. of ligroin to the pressed massand the temperature was raised to 53 C. over a period of 2 hours and wasmaintained at that point until a sample showed solubility in ethylenechloridealcohol (:10). The ester was then separated .from the reactionmixture, treated with hot water,

washed to neutrality and dried.

Example II 25 lbs. of purified cotton linters was pretreated for 16 hrs.at room temperature with a mixture of 25 lbs. of glacial acetic acid and20 lbs. of a low boiling petroleum distillate. The esterification wasthen promoted by the addition at 20 C. of a mixture of 30 lbs. ofbutyric anhydride and 40 lbs. of acetic anhydride with 1.5 lbs. of mixedcatalyst (see Example I) and 68 lbs. of a low boiling petroleumdistillate. The temperature was raised to 40 C. over a period of 2 hoursand was there maintained for 48 hrs. or until the reaction is completed.The ester was then separated from the reaction mixture, washed with hotwater and then to neutrality with cold water and dried at 50-60 C. Itwas found to be soluble in ethylene chloride-ethyl alcohol (:5). Whencoated from this solution it gave skins of good flexibility.

Example III ride-alcohol (85:15)

Example IV 50 lbs. of cotton linters was pretreated with lbs. of amixture composed of 4 parts of propionic acid and 1 part of acetic acidfor 4 hours at F. after which it was cooled to 70 F. A mixture of 150lbs. of acetic anhydride, 125 lbs. of a petroleum hydrocarbon having aboiling range of ISO-210 C., 125 lbsyof ethyl ether and 1 lb. ofconcentrated sulfuric acid was added to the pretreated mass and thetemperature was permitted to rise from 70 to 120 F. over a period of 5hours. The whole was then kept at 120 F. until a sample showed completesolubility in a mixture of 95 parts of ethylene chloride and 5 parts ofmethyl alcohol by volume. This esterification required about 10 hours.The fibers were then centrifuged and washed with ether. The non-solventretained by the fibers was removed by boiling the fibers with waterafter which they were dried.

Example V 25 lbs. of cellulose was pretreated with a mixture of '75 lbs.acetic acid, 32 lbs. of Stoddard solvent and 25 lbs. of toluene for 18hours at room temperature. The esterification Was promoted by adding amixture of lbs. of acetic anhydride, 132 lbs. of Stoddard solvent, 116lbs. of toluene and 1.5 lbs. of mixed catalyst (3 volumes phosphoric: 1volume sulfuric acid). The temperature was raised to 40 C. over a periodof 2 hours and was maintained at that point until the reaction wascomplete which required about 27 hours. The resulting cellulose acetatewas washed and dried. It was found to be soluble in methylenechloride-ethyl alcohol (90:10 by volume). Stoddard solvent is a commonlyknown petroleum distillate having a boiling range of 300-410 F., thespecifications of which are disclosed in a Bureau of Standards bulletin,Commercial standard C. S. 3-28 (1929). The pretreatment of cellulosewith a fatty acid and a non-solvent is described and claimed in Yackeland Kenyon application, Serial No. 671,898, filed of i even date.

Our process is adapted to cellulose esterification processes generallyfor the preparation of organic acid esters of cellulose. Other estersthan those of the specific examples which may be produced by our processare cellulose propionate, cellulose butyrate, cellulose acetatebutyrate, cellulose propionate butyrate, etc. The present invention isespecially adapted to the processes for preparing esters containing acylgroups of more carbon atoms than acetyl as many of the non-solventsemployed at the present time lessen in effectiveness as the proportionof those higher acyl groups increases.

Obviously the procedure in processes in accordance with our inventionmay be varied in accordance with the judgment of the individualoperator. For instance the cellulose may be treated with theesterification bath for a time before the non-solvent is added, however,it is preferred that both the diluent and the esterifying ingredients beadded together. Also the selection of the anhydride and catalyst to beemployed and the proportions thereof will not vary the present processso as to place it outside the scope of the invention. As was pointed outpreviously each homogenizer exerts its own individual homogenizingeffect in the esterification bath regardless of the presence of otherhomogenizers therein. Consequently a mixture of, a plurality ofhomogenizers might be employed if desired which mixture would exertapproximately the cumulative effect of the individual substances.

Although ethyl ether is the preferred ether for use as an homogenizerother ethers such as normal 'butyl, iso-amyl, n-propyl, etc. may beemployed as homogenizers with aliphatic hydrocarbon non-solvents infibrous cellulose esterification processes.

In some cases the aliphatic hydrocarbon may not be refined sufficientlyso that the product is rendered dark during the esterification. Whenthis occurs the product may be bleached after 'it has been separatedfrom the reaction mixture by suspending it in water containing a verysmall amount of sulfuric acid and then treating it with chlorine gas.The product formed will be almost as white as the original cotton.

The darkening of the product in a fibrous esterification process inwhich an aliphatic hydrocarbon is used may be readily avoided bysufficiently refining the hydrocarbon to remove any darkening impuritiestherefrom. This may be done by treating the hydrocarbon with fumingsulfuric acid for a time. The greater the content of sulfur trioxide inthe acid, the less time will be required for the treatment to takeplace. For example, Stoddard solvent was purified by treating it with anequal volume of fuming sulfuric acid containing 50% sulfur trioxide for48 hours at room temperature. If less acid or an acid containing lessS03 is used a longer time of treatment is required however, the time oftreatment may be reduced by using an elevated temperature.

In fibrous esterification processes in accordance with our inventionvarious cellulosic materials such as cotton fiber tissue paper, cleancotton, surgical cotton wool or bleached sulfite wood pulp which hasbeen carefully prepared, may be used. In processes carried out inaccordance with our invention refined bagasse pulp has been found to beeminently suitable for use as the starting material. In prior processeswhere bagasse was employed the products have been poor in quality andgave films which were hazy, yellow in color and of low flexibility.Bagasse pulp in a process carried out in accordance with the presentinvention, however, gives a product which compares favorably withsimilar products prepared from cotton cellulose. For example 25 gms. ofbagasse pulp were pulped with distilled water containing a trace ofnitric acid, after which the pulp was air dried and subjected topretreatment for 16 hrs. with a mixture of 25 c. 0. each of acetic acidand a petroleum distillate of a boiling range l50-200. Esterificationwas promoted by the addition of 32.5 c. 0. each of acetic and propionicanhydrides and 1 c. c. of mixed catalyst, maintaining the bath at 40 C.for 24 hrs. The product formed exhibited solubilities similar to acellulose acetate propionate prepared from cotton cellulose. It wascoated out from solution in ethylene chloride-alcohol (:5) and gave askin of good flexibility.

We claim as our invention:

1. A process for preparing an organic acid ester of cellulose in fibrousform which comprises reacting upon the cellulose with an esterifyingbath containing a lower fatty acid anhydride, a saturated hydrocarbonsubstantially boiling within the range -210" C. as the non-solvent, andan homogenizer selected from the group consisting of the lower fattyacids and the lower aliphatic ethers in suflicient amount to assurecompatibility of the ingredients of the bath, which bath will notdissolve the ester formed therein.

2. A process for preparing an organic acid ester of cellulose in fibrousform which comprises reacting upon the cellulose with an esterifyingbath containing a lower fatty acid anhydride, a saturated hydrocarbonsubstantially boiling within the range 150 210 C as th solvent, and alower fatty acid in sufficient amount to assure compatibility of theingredients of the bath, which bath will not dissolve the ester formedtherein.

3. A process for preparing an organic acid ester of cellulose in fibrousform which comprises reacting upon the cellulose with an esterifyingbath containing a lower fatty acid anhydride, a saturated hydrocarbonsubstantially boiling within the range l50-2l0 C, as th solvent, andacetic acid in sufiicient amount to assure compatibility of theingredients of the bath, which bath Will not dissolve the ester formedtherein.

4. A process for preparing cellulose acetate -propionate in fibrous formwhich comprises es- LOUIS M. MINSK. WILLIAM O. KENYON. HARRY LE B. GRAY.

